1. Field of Invention
The present invention relates to a static memory. More particularly, the present invention relates to a magnetoresistive random access memory (MRAM).
2. Description of Related Art
MRAM is a type of non-volatile memory with fast programming time and high density. A MRAM cell of giant magnetoresistance (GMR) type has two ferromagnetic layers separated by a nonmagnetic conductive layer. Information is stored as directions of magnetization vectors in the two ferromagnetic layers.
The resistance of the GMR memory cell indicates a minimum value when the magnetization vectors of the two ferromagnetic layers point in substantially the same direction. On the other hand, the resistance of the GMR memory cell indicates a maximum value when the magnetization vectors of the two ferromagnetic layers point in substantially opposite directions. Accordingly, a detection of changes in resistance allows information being stored in the MRAM cell.
In conventional MRAM architecture, MRAM cells are placed on intersections of cell lines and word lines. The cell lines and word lines connect to the peripheral circuits and/or logic circuits through metal lines and/or metal plugs disposed on the peripheral area surrounding the MRAM area. Hence, the integration density is limited.